The present invention relates to a method of verifying the external integrity of cigarettes.
In particular, the invention is pertinent to a method of the aforementioned type such as can be employed, preferably, in cigarette manufacturing machines.
It is standard practice in the art field of cigarette manufacture to verify the external integrity of the finished cigarettes by causing the single cigarettes to advance in succession, with their respective axes disposed transversely to the direction of movement, along a predetermined monitoring path extending past an optical quality control device located following a manufacturing unit in the feed direction.
The quality control device in question is designed to sample a limited number of generators delineating the outer surface of each cigarette produced, by reading images of these same sample generators and comparing each registered image with a model or reference image, to the end of indicating any superficial defects of manufacture that might be present (e.g. badly formed and/or obstructed ventilation holes, edges not gummed, incorrect positioning and/or strength of print, etc.) and thus establishing whether or not the cigarette is of acceptable quality.
The quality control device consists generally in a solid state camera with a CCD array, familiar to those skilled in the art as a Line Scan Camera, which as the name implies is designed to read an object by scanning a single line. In operation, the scan line falls on a sample generator of the outer surface presented by the cigarette passing in front of the camera at a given moment.
It is the usual practice to scan a plurality of sample generators per single cigarette, utilizing a plurality of cameras ranged along the monitoring path: accordingly, the cigarette is made to rotate around its own longitudinal axis while progressing from one camera to the next, so that a different generator will be presented to each camera in turn.
A monitoring method of the type outlined above betrays the drawback that in the event of foreign matter (such as specks of dust, particulates, tobacco filler, etc.) occupying the space in between the cigarette and the optical device during the reading operation, this is interpreted by the device as a flaw and the cigarette will be rejected even though perfectly good. In other words, it cannot be guaranteed a priori that an error signal generated by the device effectively indicates a defective cigarette on every occasion.
The drawback in question is highlighted especially in dusty surroundings, such as those in which a cigarette manufacturing machine will typically operate.
The object of the invention is to provide a method of monitoring the external integrity of cigarettes such as will remain free of the drawback described above.